1. Technical Field
The present invention relates to a capacitor that has a pressure control valve with a stable operating pressure and that is excellent in safety.
2. Background Art
FIG. 8 is a sectional view showing a conventional capacitor, and FIG. 9 is a sectional view showing a configuration of pressure control valve 23 provided in the capacitor. This capacitor includes capacitor element 20 provided with hollow 20A. Capacitor element 20 includes a pair of positive and negative electrodes, each in which a polarizable electrode layer is formed on an aluminum foil current collector, and a separator interposed therebetween (these are not shown). The positive and negative electrodes are wound in such a manner that they are displaced from each other in the opposite direction (in the vertical direction in FIG. 8). From both ends (upper and lower ends in FIG. 8) of capacitor element 20, positive and negative electrodes are electrically led out, respectively.
Case 21, which has a cylindrical shape with a bottom and is made of a metal such as aluminum, accommodates capacitor element 20 together with an electrolyte solution (not shown). Negative terminal 21A for external connection is provided integrally with the outer bottom surface of case 21. Protrusion 21B is provided integrally with the inner bottom surface of case 21 so that it is fitted into hollow 20A. After protrusion 21B is fitted into hollow 20A, the end on the side of the negative electrode of capacitor element 20 that has been inserted into case 21 is bonded to the inner bottom surface of case 21 mechanically and electrically by, for example, laser welding.
Positive terminal 22A for external connection is provided integrally with the outer surface side of aluminum sealing plate 22. Protrusion 22B is fitted into hollow 20A. Hole 22C is provided in order to pour the electrolyte solution into case 21. Pressure control valve 23 is provided so as to close hole 22C. The end on the side of the positive electrode of capacitor element 20 is bonded to the inner surface of sealing plate 22 mechanically and electrically by, for example, laser welding. Furthermore, case 21 is sealed by performing a process (curling process) so that the peripheral edge of sealing plate 22 wraps the opening portion of case 21.
As shown in FIG. 9, pressure control valve 23 includes gas permeable member 24, blocking body 25 and metal cap 26. Gas permeable member 24 and blocking body 25 are disposed on hole 22C. Metal cap 26 is provided with hole 26A that communicates with the outside. Cap 26 is fixed so as to cover them and presses blocking body 25 in the direction in which blocking body 25 always blocks hole 22C. Annular convex part 22D is provided on sealing plate 22 so that it surrounds the periphery of hole 22C. Cap 26 is fixed by deforming convex part 22D by, for example, caulking and pressing it to cap 26.
Pressure control valve 23 releases a gas generated inside the capacitor to the outside when the internal pressure of the capacitor is a predetermined pressure or more. Thus, the pressure inside the capacitor is prevented from increasing. Furthermore, after operation, pressure control valve 23 returns to its pre-operation state so as to maintain the airtightness inside the capacitor. That is to say, pressure control valve 23 is a self-returning type valve. Therefore, even if the internal pressure is increased due to the generation of gas inside the capacitor, the appearance of the capacitor is not affected, and the property can be maintained.
Furthermore, pressure control valve 23 includes gas permeable member 24. Gas permeable member 24 is formed of a material capable of preventing permeation of the electrolyte solution and allowing a gas generated inside the capacitor to permeate to the outside. By bringing gas permeable member 24 into close contact with the periphery of hole 22C of sealing plate 22, it is possible to prevent the function of pressure control valve 23 from being impaired due to contact of the electrolyte solution with blocking body 25. Furthermore, it is possible to prevent the electrolyte solution from leaking to the outside of the capacitor via pressure control valve 23. Such a capacitor is disclosed in, for example, Japanese Patent Application Unexamined Publication No. 2004-134632.
Thus, in a conventional capacitor, pressure control valve 23 is placed with respect to hole 22C for pouring an electrolyte solution into the case. Thus, it is possible to prevent leakage of an electrolyte solution. However, pressure control valve 23 is placed by directly incorporating each member on hole 22C after a capacitor is fabricated and an electrolyte solution is poured through hole 22C. Therefore, a variation in the fabrication accuracy of pressure control valve 23 leads to a variation in the operation of pressure control valve 23. In particular, since an amount of compression of blocking body 25 is directly linked to an operating pressure of pressure control valve 23, the variation in the operating pressure of pressure control valve 23 easily occurs.